X-ray apparatus

ABSTRACT

An X-ray apparatus which is readily convertible for conventional radiographic or tomographic operation includes an X-ray source and an imaging device movably supported on opposite sides of a patient support. For tomographic procedures, the source and the imaging device are interconnected by shielded drive system components to effect coordinated movement of the source and the device. For conventional radiography, the drive components are disconnected to permit independent movement of the source and the imaging device. The drive components are disconnected for conventional radiography by lowering the X-ray source and by operating a latch located near the imaging device. The drive components are connected for tomography by raising the X-ray source and by operating the latch. Other improvements such as the use of rotary encoders to provide a digital readout of the location of a tomographic examination plane and to control the operation of the source during tomographic procedures are described.

This is a continuation, of application Ser. No. 837,848 now abandonedfiled Dec. 24, 1977, which was a division of application Ser. No.603,264 filed Aug. 11, 1975, now U.S. Pat. No. 4,082,955, dated Apr. 4,1978.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to X-ray apparatus and more particulary tonovel and improved X-ray apparatus which is readily convertible foroperation in conventional radiographic and tomographic modes.

2. Prior Art

In many conventional radiographic studies, a patient lies on the surfaceof an X-ray table and an X-ray source located above the table body isenergized to direct controlled X-ray emission through a selected portionof the patient. X-radiation which has passed through the patient isincident on a film sheet carried in a Bucky or other film tray beneaththe table top. The incident radiation exposes the film sheet to form ashadow image of a portion of the patient's anatomy.

In other conventional radiographic studies, the X-ray source is directedsubstantially horizontally toward a wall mounted film holder. A patientis positioned with his chest or other body portion adjacent the filmholder and the source is energized to form a shadow image on a filmsheet carried in the holder.

In another diagnostic procedure called tomography, a patient usuallylies on the surface of the X-ray table while the X-ray source and theBucky tray move in opposite directions in spaced paths longitudinal ofthe table top. During this movement, the source and the Bucky trayessentially pivot as a unit about an imaginary axis extending through an"examination plane" within the patient. The source is rotated duringthis movement to assure that it remains directed toward the Bucky. Themovement causes images from above and below the examination plane to beblurred on the exposed film sheet, leaving as the only discernableinformation on the film, information from the examination plane.

In a multipurpose X-ray room, the X-ray apparatus must have exceptionalflexibility if it is to meet the demands of these varied procedures. Inview of the substantial costs involved in equipping and operating anX-ray room it is important that the installation be operated asefficiently as possible with minimum time being devoted to convertingthe apparatus for use from one type of procedure to another. The set-uptime required to convert prior X-ray apparatus from conventionalradiographic to tomographic use and vice versa has been unduly lengthy.Moreover, the set-up procedures have been unduly cumbersome and subjectto error.

Typical prior apparatus includes a drive bar which interconnects theX-ray source and a film tray to coordinate their movement duringtomography. The drive bar is movably supported on a pivot structurelocated between the source and the film tray. Since the source and thefilm tray must be movable independently for conventional radiographicprocedures, a means of disconnecting the drive bar from one or both ofthe source and the film tray is provided.

In order to accommodate the increases and decreases in spacing betweenthe source and the film tray which occur when the source and film trayare moved in parallel but opposite directions, the drive bar is providedwith extensible ends. Connecting the drive bar ends with the source andfilm tray during conversion from conventional radiographic totomographic operating modes necessitates that the extensible drive barbe physically aligned with and connected to other drive components whichconnect with the source and the film tray. This procedure is frequentlycumbersome and time-consuming to effect, and requires a certain degreeof strength, patience and coordination.

With some prior X-ray apparatus, the drive bar assembly is physicallyremoved and stored during conventional radiography, and must berepositioned and mechanically interconnected with other drive systemcomponents for tomography. This procedure is likewise cumbersome,time-consuming, and subject to error if the drive bar assembly isimproperly reconnected.

A further drawback of prior X-ray apparatus is that the drive bar andcertain interconnecting linkage are exposed and extend in plain viewduring operation of the apparatus. The exposure of such components isnecessitated both to facilitate access for connection and disconnectionof the components, and because if guards were provided encompassing thewide arcs through which the components move, they would be excessive insize and would greatly inhibit freedom of access to a patient positionedon the table top. The exposed operating components are unsightly andpose safety concerns. The drive bar and its interconnecting componentsare typically located in relatively close proximity to one side of thetable top and are found to inhibit ready access to a patient positionedon the table.

Exposed tomographic drive system components additionally present asanitation problem. X-radiation opaque substances such as barium arefrequently administered to a patient's digestive tract duringradiography to facilitate diagnosis. Effluents from patients undergoingthese procedures may discharge onto the apparatus and in that eventmust, of course, be cleaned up between procedures. The cleaning ofexposed, complex drive system components is time-consuming anddifficult.

Operating noise is a practical problem with some prior tomographicapparatus. The drive bar linkages provided on some prior tomographicapparatus together with other components which interconnect and guidethe movements of the source and the Bucky tray tend to generate asubstantial amount of noise as a tomograph is being produced. Theexposed nature of these drive components facilitates the transmission ofsuch noise into the surrounding environment. The sterile, accousticallyreflective surfaces commonly found in X-ray rooms do little to attenuatesuch noise.

Prior tomographic drive systems have included a spaced array ofmechanically actuated electrical switching components which areoperative as the source and the film tray move during tomography toenergize the source within a desired angular range of operation. Aproblem with this type of source control has been its complexity.Separate pairs of electrical switches have typically been required todefine each desired angular range of source operation. If a priorapparatus is provided with a capability for operating the sourceselectively in 5, 10, 20, and 40 degree ranges of operation, at leasteight switches have been provided at spaced locations to control sourceoperation in these ranges.

A further difficulty with many prior apparatus proposals has been theirfailure to provide a readily discernable and accurate readout of thelocation of the tomographic examination plane above the table top. Suchmechanical indicators, as have been used on prior apparatus, havetypically formed a part of the drive arm or its pivotal mountingstructure and, as such, have been located behind the X-ray table alongthe upstanding tower.

SUMMARY OF THE INVENTION

The present invention overcomes the foregoing and other drawbacks ofprior X-ray apparatus by providing a novel and improved X-ray apparatuswhich is readily convertible between conventional radiographic andtomographic operating modes.

An X-ray apparatus embodying the preferred practice of the inventionincludes a base and an elongated table top carried by the base. Anupstanding tower is carried by the base for movement longitudinally ofthe table top. A carriage is supported on the tower for movement alongthe tower toward and away from the table top. An extensible arm issupported on the carriage and extends over the table top. An X-raysource is supported on the extensible arm. An X-ray imaging device issupported within the base for movement longitudinally of the table top.

A novel and improved drive system is provided to interconnect and drivethe X-ray source and the imaging device through coordinated movementsfor tomography. The drive system includes components which are housedwithin and shielded by the extensible arm, by the tower, and by thebase. A proportioning arm is carried within the base and forms onecomponent of the drive system. The proportioning arm pivots about avertical axis. The location of this axis is controlled by a carriagewhich is movable to determine the ratio of the relative movementsexecuted by opposite ends of the proportioning arm as the arm pivots.

The proportioning arm is extensible and its opposite ends areconstrained to move along parallel paths, longitudinally of the tabletop. One end of the proportioning arm is releasably connected to theimaging device. The other end is connected to the upstanding tower. Asthe tower is moved longitudinally of the table top in one directionduring tomography, the proportioning arm is caused to pivot, and drivesthe imaging device a proportional distance in the opposite direction.

The drive components housed within the tower are connected to theproportioning arm and rotate in response to pivotal movement of theproportioning arm. The drive components carried within the extensiblearm are connectable to the drive components carried in the tower whenthe carriage is positioned at a predetermined location along the tower,and rotate in response to pivotal movement of the proportioning arm. Thearm-carried and the tower-carried drive components function to angulatethe X-ray source during tomography to keep the X-ray beam emanating fromthe source aligned with the imaging device.

One important feature of the apparatus of the present invention is thatthe pivotally mounted exposed drive bar used on prior apparatus has beeneliminated. The only drive components which extend vertically betweenthe table base and the overhead extensible arm are carried in andshielded by a tubular supporting column. The proportioning function ofprior drive bars is assumed by a proportioning arm which operates withinthe relatively large shielded space provided by the table pedestal.

All drive system components are in fact shielded from contact. Theimproved drive system not only eliminates the exposed drive bar used onprior apparatus to interconnect and coordinate the movement of thesource and the imaging device, but also shields and guards itscomponents enabling their operation with less noise, without detractingfrom the appearance of the apparatus and without posing safety concerns.

The tower-carried components occupy minimal space in the vicinity of thepatient and permit ready access to a patient positioned on the tabletop. The shielded nature of the drive system components inhibits patienteffluents from accumulating within the tomographic drive system, andfacilitates clean-up procedures when required.

Conversion between conventional radiographic and tomographic modes ofoperation is effected simply by energizing two electrically operateddevices, one of which moves the X-ray source along its supporting towerinto or out of a predetermined "drive interconnect position" where thetower-carried and the arm-carried drive components drivingly connect,and the other of which latches or unlatches the imaging device to thedrive system. In short, a simple, foolproof system is provided whichsubstantially automatically converts the apparatus from readiness forradiographic work to readiness for tomographic work, and vice versa.

Separate electrically operated drive systems are provided for moving thetower along the table, for moving the carriage along the tower, forextending and retracting the extensible support arm, and for positioningthe proportioning arm carriage to determine the location of the plane oftomographic examination. Separate sensors are provided to sense when thetower is centered along the table, where the carriage is positionedalong the tower, the degree of extension of the support arm, whetherarm-carried drive components are extended, and whether the Bucky tray islatched to the drive system.

The extensible arm can be rotated around the tower to perform certainradiographic procedures. A control lever is provided on the arm forreleasing a latch and for retracting certain arm-carried drivecomponents to permit rotation of the arm around the tower.

A pair of rotary encoders connect with the tomographic drive system. Oneprovides a pulsed output signal which is interpreted by a digitaldisplay system to give an accurate digital reading in millimeters of theexact location of the examination plane. The other provides a pulsedoutput signal which is used to energize the X-ray source within one ofseveral predetermined angular ranges of operation.

An object of the invention is to provide an X-ray apparatus which isreadily operable in both radiographic and tomographic modes.

Another object is to provide a tomographic X-ray apparatus having anovel and improved drive system.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an X-ray apparatus constructed inaccordance with the preferred practice of the present invention;

FIGS. 2 and 3 are enlarged sectional views as seen from planes indicatedby lines 2--2 and 3--3 in FIG. 1;

FIG. 4 is a sectional view showing a portion of FIG. 3 on an enlargedscale;

FIGS. 5 and 6 are sectional views as seen from planes indicated by lines5--5 and 6--6 in FIG. 4;

FIGS. 7 and 8 are sectional views as seen from planes indicated by lines7--7 and 8--8 in FIG. 3;

FIG. 9 is an enlarged view of a portion of the structure shown in FIG. 2with some portions broken away to illustrate details of construction;

FIG. 10 is an enlarged perspective schematic view illustrating therelationship of several components of the structure shown in FIG. 3;

FIG. 11 is an enlarged view of a portion of the structure shown in FIG.2 with some portions broken away to illustrate details of construction;

FIG. 12 is a sectional view as seen from a plane indicated by a line12--12 in FIG. 11;

FIG. 13 is a schematic front elevational view of portions of theapparatus shown in FIG. 1;

FIG. 14 is a schematic top plan view of portions of the apparatus shownin FIG. 1;

FIG. 15 is an enlarged schematic top plan view of portions of theapparatus shown in FIGS. 1 and 14;

FIG. 16 is a sectional view of one of the rotary encoders shown in FIG.15, as seen from a plane indicated by a line 16--16 in FIG. 15; and

FIGS. 17 and 18 are top plan views of two discs used in separate ones ofthe rotary encoders shown in FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an X-ray apparatus is indicated generally by thenumeral 20. The apparatus 20 includes a table top 21 supported on a baseor pedestal 22. A tower 23 is carried by the pedestal 22 for movementlongitudinally of the table top 21. A carriage 24 is supported on thetower 23 for vertical movement along the tower 23. An extensible supportarm 25 is connected to the carriage 24 and supports an X-ray source 26including a collimator 27. Suitable power cables 28 extend up through atubular conduit 29 at the rear of the tower 23 and connect with theX-ray source 26.

Referring to FIG. 2, a film cassette holder 30 called a Bucky tray issupported beneath the table top 21. In operation, X-radiation emitted bythe source 26 passes through portions of a patient positioned on thetable top 21 and forms an image on a cassette-carried film sheetsupported in the Bucky tray 30.

I. The Tower 23

The tower 23 is supported on a base carriage 40 for movementlongitudinally of the table top 21. Referring to FIG. 2, the basecarriage 40 is interposed between the pedestal 22 and the tower 23. Thecarriage 40 includes a framework having top and bottom walls, 41, 42, afront wall 43, and a rear wall 44. A plurality of rollers 45 arerotatably carried on the front wall 43. The rollers 45 have a V-shapedperipheral grooves 46.

A track 50 is carried by the pedestal 22. A mounting plate 51 forms partof the pedestal 22 and extends longitudinally beneath the table top 21,as shown in FIG. 1. A plurality of spacers 52 rigidly connect themounting plate and the track 50.

The rollers 45 ride along opposite sides of the track 50. The top andbottom sides of the track are provided with V-shaped surfaces 53 whichextend into the roller grooves 46. The interconnection between therollers 45 and the track 50 mounts the base carriage 40 for movementlongitudinally of the table top 21.

A toothed gear rack 54 is carried on the track 50 and extendslongitudinally along the track 50. A reversible drive motor 55 issupported inside the base carriage 40 and has a drive shaft 56. Thedrive shaft 56 projects through a hole 57 formed in the front wall 43. Atoothed gear 58 is secured to the drive shaft 56 and drivingly engagesthe gear rack 54. When the drive shaft 56 rotates in one direction, thebase carriage 40 moves rightwardly along the track 50, as viewed inFIG. 1. When the motor 55 rotates the shaft 56 in the oppositedirection, the base carriage moves leftwardly along the track 50.

Referring to FIGS. 2 and 3, the tower 23 includes an upstanding tubularcolumn 60 which is generally square in cross-section. The column 60 issecured to the rear wall 44 of the base carriage 40. A mounting plate 61extends vertically within the column 60, dividing the column 60 into twoelongated chambers 62, 63.

Referring to FIGS. 3 and 4 a cover 64 interconnects the upper end of thecolumn 60 and the conduit 29. The conduit 29 is of rectangularcross-section and extends through a hole 65 formed in the cover 64. Athreaded fastener 66 extends through aligned holes formed in the cover64 and in the conduit 29 to secure the cover 64 to the conduit 29.Threaded fasteners 67 extend through holes formed in the cover 64 andare threaded into the mounting plate 61 to secure the cover 64 to themounting plate 61.

II. The Carriage 24

The carriage 24 includes top and bottom covers 71, 72. Openings 73, 74are formed through the covers 71, 72 to receive the column 60. Upper andlower support plates 75, 76 are positioned inside the covers 71, 72.Openings 77, 78 are formed through the plates 75, 76 to receive thecolumn 60. The covers 71, 72 and the plates 75, 76 cooperate to define apair of chambers 79, 80 that perimetrically surround the column 60.

Upper and lower sets of rollers 81, 82 are provided within the chambers79, 80 to movably support the carriage 24 on the column 60. Upper andlower bracket assemblies 83, 84 rotatably support the rollers 81, 82.The bracket assemblies 83, 84 include set screws 85, 86 to position therollers 81, 82 transversely of the column 60 so that the rollers 81, 82will snugly engage the periphery of the column 60.

A cylindrical collar 90 interconnects the support plates 75, 76. Thecollar 90 has a longitudinally extending circular bore 91. The plates75, 76 have annular flanges 93, 94 which extend into the ends of thebore 91. Threaded fasteners, not shown, secure the plates 75, 76 to thecollar 90.

A cable and pulley system supports the carriage 24 for vertical movementalong the tower 23. Referring to FIGS. 4 and 5, a pair of cables 100have end regions 101 which extend through a pair of holes 102 formed inthe lower support plate 76. A pair of cable end clamps 103 retain thecable end regions 101 in the holes 102.

The cables 100 have reaches 104 which extend upwardly alongside acarriage locking assembly 105, and are reeved around a pair of pulleys106. A shaft 107 mounts the pulleys 106. Bearing blocks 108 journalopposite end portions of the shaft 107. Threaded fasteners 109 securethe bearing blocks 108 to the mounting plate 63. The pulleys 106 extendthrough an opening 110 formed in the mounting plate 61.

Two pairs of idler rollers 111, 112 are provided in the upper end of thechamber 62 to widen the distance between the cables 100 as they dependfurther into the chamber 62. The rollers 111 are relatively closelyspaced rollers which receive the cables 100 as they depend from thepulleys 106. The rollers 112 are relatively widely spaced rollers whichwiden the distance between the cables 100 to that shown in FIG. 6.

A pair of stub shafts 113 journal the rollers 111. The stub shafts 113have threaded end regions 114 which extend through holes formed in themounting plate 61. Threaded fasteners 115 secure the stub shafts 113 inplace on the mounting plate 61.

A pair of stub shafts 117 journal the rollers 112. The stub shafts 117are secured to a plate 118 by threaded fasteners 119. A pair of brackets120, 121 are secured to upper and lower end regions of the plate 118.Threaded fasteners 122 mount the brackets 120, 121 on the mounting plate61.

Referring to FIG. 2, the cables 100 depend through the chamber 62 andhave ends secured to a bracket 123. The bracket 123 is threaded toreceive a threaded rod 124. A pair of bearing blocks 125 are secured tothe mounting plate 61 and journal the rod 124 for rotation.

A reversible drive motor 126 is mounted within the base carriage 40 forraising and lowering the carriage 24 along the tower 23. The motor 126has a drive shaft 127 which depends through an opening 128 formed in thebottom wall 42. A pulley 129 is mounted on the drive shaft 127. A drivebelt 130 is reeved around the pulley 129 and around a pulley 131 securedto the threaded rod 124. When the motor 126 rotates the threaded rod 124in one drive direction, the bracket 123 moves up the rod 124, causingthe carriage 24 to move downwardly along the tower 23. When the motor126 rotates the threaded rod 124 in the opposite drive direction, thebracket 123 moves down the rod 124, causing the carriage 24 to moveupwardly along the tower 23.

The carriage locking assembly 105 is operable in the event of failure ofthe cables 100 to arrest downward movement of the carriage 24 along thecolumn 23. Referring to FIGS. 4 and 5, the carriage locking assemblyincludes a bracket 132 mounted on the inner wall of the collar 90. Apair of surfaces 133 defining inclined trackways facing toward thecolumn 60 are formed on the bracket 132. Upper and lower stop surfaces134, 135 are provided at opposite ends of the trackway surfaces 133.

A pair of rollers 136 are positioned between the stops 134, 135 adjacentthe trackways 133. A roller support bracket 137 rotatably carries therollers 136.

A pair of tension coil springs 138 have their upper end regionsconnected to the upper end region of the bracket 132. A T-shaped member139 connects with the lower end regions of the springs 140 and has astem portion which depends through and is clamped by the roller supportbracket 137. A flexible cable 140 connects with the lower end region ofthe T-shaped member 139 and is reeved around a pulley 141 carried on thelower end region of the bracket 132. A reach of the cable 140 extendsupwardly from the pulley 141 and is secured to a cable clamping bracket142.

The cable clamping bracket 142 clamps the cables 100 at a position abovethe bracket 132, securing the cables 100, 140 together for concurrentmovement. The cable clamping bracket 142 is positioned on the cables 100at a location which will extend the tension coil springs 138 and whichwill position the rollers 136 near the lower stop surfaces 135.

If one or both of the cables 100 should fail, the clamping bracket 142will no longer be held upwardly by the cables 100. The springs 138 willthen be operative to move the rollers 136 rapidly upwardly along thetrackways 133 and into wedging engagement with the outer surface of thecolumn 60. The wedging engagement between the rollers 136 and the column60 will arest downward movement of the carriage 24, thereby preventingthe carriage 24, the extensible arm 25, and the X-ray source 26 fromdropping any significant distance toward the table top 21.

III. The Extensible Arm 25

Referring to FIG. 3, the extensible support arm 25 includes a housing143. The housing 143 is supported on the collar 90 for limited rotationaround the column 60. A pair of annular bearing rings 144 are carried intop and bottom ends of the housing 143 to journal the collar 90.

A releasable lock is provided to facilitate the retention of theextensible arm 25 in an attitude extending forwardly of the tower 23.This lock remains engaged during tomographic procedures and during allradiographic procedures except when the arm 25 must be rotated aroundthe column 60 to position the source 26 for a special radiographicprocedure.

Referring to FIGS. 3, 4 and 6 the lock includes a locking pin 145carried in the arm 25, and an apertured block 146 carried by the collar90. When the locking pin 145 is latched in engagement with the lockingblock 146, as shown in FIGS. 4 and 6, the arm 25 cannot rotate aroundthe column 60. When the locking pin 145 disengages the locking block146, the arm 25 is rotatable about the collar 90. The mechanism whichunlatches the locking pin 145 will be described later.

The housing 143 projects forwardly of the tower 23 to overlie the tabletop 21. An upwardly facing opening 147 is formed in the housing 143. Acover plate 148 closes the opening 147. A forwardly facing opening 149is provided in the forward end of the housing 143.

An extensible arm section 150 is telescopically carried by the housing143. The arm section 150 includes a tubular member 151 which extendsthrough the opening 149. A plurality of rollers 152 are carried insidethe housing 143. The rollers 152 engage the peripheral surface of thetubular member 151 to support the arm section 150 for telescopicmovement relative to the housing 143.

A sleeve 155 is carried by the tubular member 151. The sleeve 155 has atubular portion 156 which extends into the forward end of the tubularmember 151, and a flange portion 157 located forwardly of the tubularmember 151. A pair of bushings 158 are provided inside opposite endregions of the sleeve 155.

A hollow shaft 160 extends through the bushings 158. A mounting block161 is connected on one end region of the shaft 160. The X-ray source 26is supported on the mounting block 161. A collar 162 is carried near theopposite end region of the shaft 160. The mounting block 161 and thecollar 162 engage outer ends of the bushings 158 and inhibit axialmovement of the shaft 160 relative to the arm section 150.

A reversible drive motor 163 is supported within the housing 143. A ballbearing speed reducer 164 drivingly connects the motor 163 to a threadedrod 165. A nut 166 is threaded onto the rod 165. A bracket 167 mountsthe nut 166 on the inner end region of the tubular member 151. When themotor 163 rotates the threaded rod 165 in one direction, the nut 166moves leftwardly along the rod 165, as viewed in FIG. 3, causing the armsection 150 to extend leftwardly relative to the housing 143. When themotor 163 rotates the rod 165 in the opposite direction, the nut 166moves rightwardly along the rod 165, drawing the arm section 150inwardly of the housing 143.

IV. The X-ray Source 26

The X-ray source 26 is movable relative to the table top 21 in fiveindependent ways:

(1) Through movement of the tower 23 longitudinally of the table top 21,as has been described;

(2) Through movement of the carriage 24 vertically along the tower 23,as has been described;

(3) Through rotation of the arm 25 on the carriage 24 about the verticalaxis of the column 60, as has been described;

(4) Through extension and retraction of the extensible arm 25 laterallyof the table top 21, as has been described; and

(5) Through rotation about the axis of the hollow shaft 160, as will nowbe described.

The shaft 160 is journaled for rotation by the bushings 158. The X-raysource 26 is rotatable with the shaft 160 through an angle of 180degrees between horizontal attitudes. Two devices are operative toinhibit rotation of the X-ray source about the axis of the shaft 160.One of these devices is a friction brake 170. The other is a detentassembly 179.

Referring to FIGS. 7 and 8, the friction brake 170 is an assembly whichis interposed between the X-ray source 26 and the extensible arm 25 tohold the X-ray source 26 in a selected rotary orientation. An aperture171 is provided in the mounting block 161 facing toward the flange 157.A tubular housing 172 is pressed into the aperture 171. A set screw 173is threaded into one end region of the tubular housing 172. A plunger174 is slidably carried in the other end region of the housing 171. Acompression coil 175 spring is interposed between the set screw 173 andthe plunger 174 and biases the plunger 174 toward the flange 157.

Friction brake material in the form of a braking pad 176 is carried onthe plunger 174. The brake pad 176 is engagable with an annular ring 177carried on the flange 157.

The drag force provided by the friction brake 170 as the plunger-carriedbraking pad 176 drags along the ring 177 is easily adjusted by threadingthe set screw 173 into or out of the tubular housing 172. The set screw173 is adjusted to provide a drag force sufficient to hold the X-raysource 26 in a selected position, but which will still permit anoperator to rotate the source 26 easily. Once the set screw 173 isproperly adjusted, it is locked in place by tightening a locking nut 178into engagement with one end of the housing 172.

Referring again to FIGS. 7 and 8, the detent assembly 179 facilitatespositioning the X-ray source in vertical and horizontal attitudes. Threedetent notches 180, 181, 182 are provided in the ring 177. The notches180, 182 correspond to horizontal orientations of the X-ray source 26.The notch 181 is used for downward vertical orientation of the source26.

Referring to FIG. 7, a detent lever 185 is provided for selectivelyengaging the notches 180, 181, 182. The lever 185 extends through a hole186 formed in the mounting block 161. A pin 187 extends through one endregion of the lever 185 and pivotally mounts the lever 185 for movementabout the axis of the pin 187. A detent projection 188 is formed on theopposite end region of the lever 185 for engaging the notches 180, 181,182.

An arm 190 has one end rigidly connected to the lever 185. A compressioncoil spring 192 is interposed between the arm 190 and the mounting block161. The compression spring 192 biases the arm 190 and the lever 185counterclockwise as viewed in FIG. 7 to urge the detent projection 188in one of the notches 180, 181, 182.

An electrically operated solenoid 195 is provided to pivot the arm 190and the lever 185 clockwise to move the projection 188 out of one of thenotches 180, 181, 182. A bracket 196 supports the solenoid 195 insidethe hollow shaft 160. The solenoid 195 has an armature 197 which ismovable axially of the hollow shaft 160. A tension coil spring 191interconnects one end of the arm 190 and the armature 197. When thesolenoid 195 is electrically energized, the armature 197 moves axiallyinwardly of the hollow shaft 160, pivoting the arm 190 against theaction of the compression spring 192 and releasing the detent projection188 from one of the notches 180, 181, 182.

V. Driven Movement of the X-ray Source 26 and the Bucky Tray 30

If a tomograph is to be made with the X-ray apparatus 20, the X-raysource 26 and the Bucky tray 30 are driven back and forth in oppositedirections longitudinally of the table top 21. Simultaneously with suchlongitudinal movement, the source 26 is rotated about the axis of thehollow shaft 160 to keep the X-ray beam centered on a target area withina patient positioned on the table top 21.

Translation of the source 26 longitudinally of the table top 21 iseffected by moving the tower 23 along the track 50. The reversible drivemotor 55 (FIG. 2) is energized alternately in forward and reverse modesto effect this movement.

Rotation of the source 26 in coordination with its translation, andreciprocation of the Bucky tray 30 are effected by a drive system havinginterconnected components located in the table pedestal 22, in the tower23, and in the extensible support arm 25.

A. The Arm-carried Drive Components

Referring to FIG. 3, a telescoping drive shaft 200 extends through theextensible arm 25. The shaft 200 includes a hollow tubular section 201and a solid inner section 202. A universal joint 203 connects the innershaft section 202 to the hollow shaft 160. A bearing block 204 issupported by the housing 143 and slidably journals the hollow section201. A pair of spaced collars 208, 210 are mounted on the hollow shaftsection 201.

The hollow shaft section 201 is movable axially relative to the bearingblock 204. When the hollow shaft section 201 is positioned as shown inFIG. 3, it is in what will be called its "retracted" position. As willbe explained, when the shaft section 201 is retracted, it isdisconnected from a drive system carried in the column 60.

When the shaft section 201 is positioned such that the collar 210 abutsthe bearing block 204, the shaft section is in what will be called its"extended" position. The shaft section 201 is normally kept in itsextended position and is retracted only when it is necessary to rotatethe extensible arm about the collar 90 for a special radiographicprocedure. As will be explained, when the shaft section 201 is extended,it in no way hinders movement of the carriage 24 vertically along thetower 23.

Movement of the shaft section 201 between its extended and retractedpositions is effected by operating a lever 220. Referring to FIGS. 3 and10, the lever 220 is located on the underside of the housing 143. Ashaft 221 connects with the lever 220 and extends upwardly through anopening in the housing 143.

Referring to FIG. 10, a cam 222 is mounted on the upper end region ofthe shaft 221. An L-shaped arm 223 is pivoted at 224. A tension coilspring 225 biases the L-shaped arm into engagement with the cam 222.Rotation of the lever 220 will cause the cam 222 to pivot the arm 223,causing extension and contraction of the spring 225.

A connector 230 is carried on the tubular section 201. A circumferentialgroove 209 is formed in the connector 230. A yoke 226 extends into thegroove 209. A rod 227 interconnects the yoke 226 and the L-shaped arm223. When the arm 223 is pivoted by the cam 222, the rod 227 pushes orpulls the yoke 226 to move the tubular shaft section 201 between itsextended and retracted positions.

The connector 230 carries a groove 231 which extends diametrically ofthe shaft section 201. When the X-ray source 26 is oriented verticallydownwardly, the groove 231 extends vertically. Referring to FIG. 3, whenthe shaft section 201 is extended, the connector 230 projects through anopening 233 formed in the collar 90, but does not project through analigned opening 234 formed in the column 60. When the shaft section 201is retracted, the connector 230 is withdrawn from the opening 233.

The positioning of the locking pin 145 is controlled by the lever 220.Referring to FIG. 3, the locking pin 145 is slidably carried by thebearing block 204. A bracket 240 is connected to the locking pin 145 andextends upwardly to a position between the collars 208, 210. A tensioncoil spring 241 is secured at opposite ends to the bearing block 204 andthe bracket 240. The spring 241 biases the locking pin 145 toward aposition of engagement with the locking block 146.

When the tubular shaft 201 is retracted, as by moving the lever 220 tothe positions shown in FIGS. 3 and 10, the collar 210 engages thebracket 240 and pulls the pin 145 out of engagement with the lockingblock 146. When the tubular shaft 201 is extended, as shown in FIG. 4,the collar 210 disengages the bracket 240 and permits the spring 241 tomove the locking pin 145 into engagement with the locking block 146.

B. The Column-carried Drive Components

Referring to FIGS. 2, 3 and 4, a hollow tubular drive shaft 250 extendsvertically within the column chamber 63. A bearing block 252 is securedto the mounting plate 61 and journals the lower end of the shaft 250. Ashaft extension 253 is welded to the upper end of the shaft 250. A pairof bushings 254, 255 are carried by the brackets 120, 121 and journalthe shaft extension 253.

Referring to FIGS. 3 and 4, a miter gear segment 260 is carried on theshaft extension 253 at a location between the brackets 120, 121. A mitergear 261 meshes with the miter gear segment 260. A stub shaft 262 isrigidly connected to the miter gear 261. A pair of bushings 263, 264journal the miter gear 261 and the stub shaft 262 for rotation about ahorizontal axis. The bushing 263 is supported by the plate 118. Abracket 265 is welded to the bracket 121 and supports the bushing 264.

A connector 270 is carried on the stub shaft 262 adjacent the miter gear261. As is best seen in FIG. 10, the connector 270 is provided with atongue 271 adapted to extend into the groove 231 of the connector 230when the connector 230 is extended through the opening 233. As will beexplained, when the base carriage 40 positions the tower 23 centrallyalong the table top 21, the groove 231 extends vertically. When thetongue 271 of the connector 270 engages the groove 231 of the connector230, a driving connection is established that will cause the X-raysource 26 to rotate about the axis of the hollow shaft 160 in responseto rotation of the column-carried drive shaft 250.

Referring to FIG. 2, a mounting bracket 280 is secured to the lower endregion of the column 60. A vertically extending pin 281 is journaled bythe bracket 280. An upper arm 282 and a lower arm 283 are pivotallymounted by the pin 281 for rotation about a vertical axis indicated bythe numeral 284. The lower arm 283 is a tubular duct for guiding thepower cables 28 from the pedestal 22 to the lower end of the tubularconduit 24.

A pair of fan gears 285, 286 drivingly connect the upper arm 282 and thedrive shaft 250. The fan gear 285 is connected to the lower end regionof the drive shaft 250. The fan gear 286 is connected to the upper arm282. The fan gears 285, 286 are identical in construction and areoperative to rotate the shaft 250 in response to rotation of the upperarm 282 about the axis 284.

C. The Pedestal-carried Drive Components

Referring to FIG. 2, a mounting plate 300 is rigidly supported in thebase of the pedestal 22. A pair of spaced bearing blocks 301, 302 and areversible drive motor 303 are supported atop the mounting plate 300. Athreaded rod 304 is journaled by the bearing blocks 301, 302. A ballbearing speed reducer 305 drivingly connects the motor 303 and thethreaded rod 304.

The ball bearing speed reducer 305 is of identical construction to thespeed reducer 164 which drivingly interconnects the arm extension motor163 and the arm extension rod 165. Referring to FIG. 9, the speedreducer 305 includes a cylindrical housing 306. The threaded rod 304 hasa reduced diameter end region 307 which projects into one end of thehousing 306. The motor 303 has a drive shaft 308 which projectscoaxially into the opposite end of the housing 306.

A pair of ball bearings 310, 311 are carried in the housing 306. Thebearings 310, 311 have inner races 310a, 311a, outer races 310b, 311b, aplurality of balls 310c, 311c interposed between the races 310a, 311aand 310b, 311b, and ball cages 310d, 311d which circumferentially spacethe balls 310c, 310d around the inner races 310a, 311a.

A bushing 312 is interposed between and drivingly connects the innerrace 310a and the motor drive shaft 308. A sleeve 313 drivinglyinterconnects the cage 310d and the inner race 311a. A sleeve 314drivingly interconnects the cage 311d and the rod end region 307.

Three pairs of set screws 315 (only one pair is shown in FIG. 9) arethreaded into apertures 316 formed in the housing 306. The pairs of setscrews 315 are equally spaced circumferentially of the housing 306. Theinner ends of the set screws 315 engage the outer races 310b, 311b andprevent relative rotation between the outer races 310b, 311b and thehousing 306. By adjusting the torque to which the set screws 315 aretightened into engagement with the outer races 310b, 311b, the preloadforce applied to the bearing balls 310c, 311c is controlled. Lock nuts317 secure the set screws 315 in place once the desired torque has beenapplied to the set screws 315.

The speed reducer 305 is operable to effect approximately a 7 to 1 speedreduction. The inner race 310a rotates at 21/2 times the speed of thecage 310d. The inner race 311a rotates at about 21/2 times the speed ofthe cage 311d. The threaded rod 304 accordingly rotates at aboutone-seventh the speed of the motor drive shaft 308.

Referring to FIGS. 2 and 15, a carriage 320 is supported on the threadedrod 304. The carriage 320 includes a threaded nut 321 which is threadedonto the rod 304. A plate 319 is supported atop the nut 321. When themotor 303 rotates the threaded rod 304 in one direction, the carriage320 moves leftwardly (as viewed in FIG. 2) along the rod 304. When themotor 303 rotates the rod 304 in the opposite direction, the carriage320 moves rightwardly along the rod 304.

A vertically extending pivot pin 325 is journaled by the carriage 320. Asprocket 328 is secured to the lower end region of the pivot pin 325. Aswivel plate 326 is mounted on the upper end region of the pin 325 forrotation together with the sprocket 328 about an axis indicated by thenumeral 327.

A roller chain 328a is reeved around the sprocket 328 and around asprocket 329. The sprocket 329 is rotatably carried by an encoderassembly 330. The encoder assembly 330 is supported on the plate 319 andoperates to monitor the pivotal movement of the swivel plate 326relative to the carriage 320 as will be explained in Section VII of thisspecification.

The effect of moving the carriage 320 leftwardly or rightwardly alongthe threaded rod 304 is to vary the distance, as measured laterally ofthe table top 21, between the axes 284, 327. This laterally measureddistance is indicated by the reference character A in FIG. 2. While thetrue distance between the axes 284, 327 will vary as the column 23 moveslongitudinally of the table top 21, the laterally measured component Aof the true distance is solely a function of the positioning of thecarriage 320 by the motor 303.

Referring to FIG. 15, the position of the carriage 320 along thethreaded rod 304 is monitored by a rotary encoder assembly 336. Theencoder assembly 336 is supported on the mouting plate 300 and carries arotatable sprocket 337. A roller chain 338 is reeved around the sprocket337 and around a sprocket 339. The sprocket 339 is supported on thethreaded rod 304 and serves to drive the encoder sprocket 337. Theencoder assembly 336 monitors the position of the carriage 320 as willbe described in Section VI of the specification.

A total of eight rollers are carried on the swivel plate 326. Theserollers are positioned in laterally spaced pairs 331, 332, 333, 334, andonly one roller from each pair appears in FIG. 2. The roller pairs 331,332 engage opposite sides of the upper arm 282. The roller pairs 333,334 engage opposite sides of an arm 335.

The roller pairs 331, 332 effectively establish a sliding connectionbetween the swivel plate 326 and the upper arm 282. As the tower 23moves longitudinally of the table top 21 in response to operation of thebase carriage drive motor 55, the sliding connection between the swivelplate 326 and the upper arm will cause the swivel plate to pivot aboutthe axis 327, and will cause the upper arm 282 to pivot about the axis284. As the upper arm 282 pivots about the axis 284, the fan gears 285,286 effect corresponding rotation of the drive shaft 250.

The roller pairs 333, 334 operate to rotate the arm 335 concurrentlywith the swivel plate 326, while permitting relative sliding movementbetween the arm 335 and the swivel plate 326. The roller pairs 331, 332,333, 334 are arranged such that the paths of permitted relative slidingmovement between the arms 335, 282 and the swivel plate 326 are paralleland intersect the axes 327, 284.

A linear cam member 340 is supported by the pedestal 22. The cam member340 extends longitudinally of the table top 21 and defines a downwardlyopening, longitudinally extending recess 341. A pin 342 is carried onthe forward end region of the arm 335 and extends into the recess 341.The pin 342 has an axis indicated generally by the numeral 343. The pin342 and the recess 341 establish a sliding, pin-in-slot connection whichmaintains the axis 343 laterally fixed relative to the table top 21 asthe arms 335, 282 rotate during movement of the tower 23 longitudinallyof the table top 21.

D. The Bucky Tray Drive System

The movement of the pin 342 longitudinally of the table top 21 isutilized to drive the Bucky tray 30 longitudinally of the table top 21during tomographic procedures. As will be explained in greater detail,the lateral distance between the axes 343, 327 determines the distancethrough which the Bucky tray 30 will be moved longitudinally of thetable top 21 in response to movement of the tower 23 through a givenlongitudinal distance.

The lateral distance between the axes 343, 327 is indicated in FIG. 2 bythe reference character B. As the distance B increases, the distancelongitudinal of the table top through which the pin 342 is caused tomove (as the tower 23 moves a given distance) will increase. As thedistance B decreases, the distance longitudinal of the table top throughwhich the pin 342 is caused to move (as the tower 23 moves a givendistance) will decrease.

The mechanism which transmits motion from the pin 342 to the Bucky tray30 includes a welded, U-shaped arm 350. The arm 350 has parallel,overlying upper and lower portions 351, 352 which are interconnected bya cylindrical central stem portion 353.

A pair of vertically spaced bearing blocks 355 are mounted on themounting plate 51. The stem portion 353 of the U-shaped arm 350 has endregions 356 which are journaled by the bearing blocks 355. The bearingblocks 355 pivotally support the arm 350 for movement about the axis ofthe stem portion 353.

A sliding bearing 360 is carried on the distal end of the lower armportion 352. A slide 361 is slidably carried in the bearing for movementlongitudinal of the lower arm portion 352. The slide 361 is pivotallyconnected to the pin 342. As the pin 342 reciprocates longitudinally ofthe table top 21, the connection between the slide 361 and the lower armportion 352 causes the arm 350 to pivot about the axis of the stemportion 353.

A Bucky tray drive bar 365 is positioned above the upper arm portion351. The bar 365 is pivotally carried on the upper stem end region 356and is pivotal about the axis of the stem portion 353 independent of themovement of the U-shaped arm 350.

The Bucky tray 30 is supported in a carriage 366. The carriage 366 issupported on bearings, not shown, and is constrained such that it canonly move longitudinally of the table top 21. A pin 367 depends from thecarriage 366 and extends into a slot 368 formed in the Bucky tray drivebar 365. The axis of the pin 367 is coaxial with the axis 343 of the pin342. When the Bucky tray drive arm 350 pivots about the axis of the stemportion 353 in response to movement of the pin 342, the movement of thepin 342 is transmitted to the pin 367 causing the Bucky tray 30 to movelongitudinally of the table top 21.

A solenoid operated latch, indicated generally by the numeral 370, iscarried on the upper arm portion 351 and is operable to selectivelyconnect and disconnect the upper arm portion 351 and the drive bar 365.When the upper arm portion 351 and the drive bar 365 are connected bythe latch 370, they pivot together about the axis of the stem portion353 in response to longitudinal movement of the tower 23 along the tabletop 21. When the upper arm portion 351 and the drive bar 365 aredisconnected by the latch 370, longitudinal movement of the tower 23will have no driving effect on the Bucky tray drive bar 365.

Referring to FIG. 11, the solenoid operated latch 370 includes asolenoid 371. A bracket 372 mounts the solenoid 371 on the upper armportion 351. The solenoid 371 has an armature 373 which is normallyextended to the position shown in FIG. 11. When the solenoid 371 iselectrically energized, it moves the armature 373 rightwardly, as viewedin FIG. 11.

A mounting block 374 is supported on the upper arm portion 351 at aposition above the armature 373. Threaded fasteners 375 secure themounting block 374 to the arm portion 351. A pin 376 is carried by themounting block 374. A latch pawl 377 is pivotally supported on the pin376. A tension coil spring 378 is connected at one end to the pawl 377and at its other end to a pin 379 supported in the mounting block 374.The spring 378 biases the pawl 377 clockwise, as viewed in FIG. 11toward a position where the pawl 377 abuts the end of the arm portion351.

A tension coil spring 380 interconnects the pawl 377 and the armature373. When the solenoid 371 is energized to move the armature 373rightwardly, as viewed in FIG. 11, the spring 380 is operative to pivotthe pawl 377 counterclockwise to the position shown in phantom in FIG.11.

Referring to FIGS. 11 and 12, latching block 385 is supported on theBucky drive bar 365 by threaded fasteners 386. A forwardly facing notch387 is formed in the latching block 385. When the pawl 377 is receivedin the notch 387, as when the solenoid 371 is de-energized, the Buckytray drive bar 365 and the upper arm portion 351 are latched together.When the pawl 377 is pivoted to the position shown in phantom in FIG.11, as when the solenoid 371 is energized, the pawl 377 is not receivedin the notch 387, and relative movement is permitted between the upperarm portion 351 and the Bucky tray drive bar 365.

Positioning the pawl 377 in the notch 387 is facilitated by inclinedsurfaces 388 formed on the mounting block 385 on opposite sides of thenotch 387. When the solenoid 377 is de-energized, movement of the Buckytray drive bar 365 toward a position overlying the upper arm portion 351will bring the pawl 377 into engagement with one of the surfaces 388. Asthe Bucky tray drive bar continues to move toward a position overlyingthe upper arm portion 351, the surface 388 engaged by the pawl 377 willpivot the pawl 377 in opposition to the action of the spring 378. As thedrive bar 365 reaches a position overlying the upper arm portion 351,the pawl 377 will pivot into the notch 387, locking the drive bar 365 tothe upper arm portion 351.

E. Position Sensors and Safety Interlocks

Before a tomograph can be made with the X-ray apparatus 20, severalconditions must be met:

(1) The tube rotation detent assembly 179 must be unlatched to permitrotation of the X-ray source 26 about the axis of the shaft 160:

(2) The extensible arm 25 must be properly retracted to position theX-ray source 26 in a centered position above the Bucky tray 30;

(3) The arm 25 must be positioned forwardly to extend over the table top21;

(4) The carriage 24 must be positioned at the proper height above thetable top to permit connection between the connectors 230, 270;

(5) The connectors 230, 270 must be connected to transmit rotation fromthe vertical shaft 250 to the horizontal drive shaft 200;

(6) The Bucky tray drive arm 365 must be connected by the pawl 377 tothe upper arm portion 351; and,

(7) The base carriage 40 must be properly positioned longitudinally ofthe table top 21.

Sensors are preferably provided for sensing compliance with all of theseconditions.

Referring to FIG. 7, a limit switch 390 is carried within the mountingblock 161 to sense when the detent projection 188 is engaging one of thenotches 180, 181, 182. The switch 390 is positioned to be engaged by thearm 190 when the detent projection 188 is engaging one of the notches180, 181, 182, and to be disengaged by the arm 190 when the detentprojection 188 is out of the notches 180, 181, 182. By this arrangement,the switch 390 provides a variation in an electrical signal indicativeof when the detent assembly 179 has unlatched to permit rotation of theX-ray source about the axis of the shaft 160.

Referring to FIG. 3, a limit switch 391 is carried within the housing143. An inclined cam surface 392 is provided atop the tubular member151. The switch 391 is positioned to be engaged by the cam 392 andprovides a variation in an electrical signal indicative of when theextensible arm 25 is properly retracted to a centered position fortomographic operation.

Referring again to FIG. 3, a limit switch 393 is carried within thehousing 143. The switch 393 is positioned to be engaged by the collar210 when the extensible tubular shaft section 201 has extended, and tobe disengaged by the collar 210 when the shaft section 201 is retracted.By this arrangement, the switch 393 provides a variation in anelectrical signal indicative of when the arm 25 is locked in a forwardposition.

Referring to FIG. 2, a pair of limit switches 394, 395 are carriedwithin the column 60. The switches 394, 395 are positioned to be engagedby the nut 123 as the nut moves along the threaded rod 124. The switch394 is positioned above the switch 395 and is operative to provide avariation in an electrical signal when the carriage 24 is positioned twoinches below the location where the connector 230 makes drivingconnection with the connector 270 when the tubular shaft section 201 isextended. The switch 395 provides a variation in an electrical signal inresponse to positioning of the carriage 24 at the proper height wheredriving connection is established between the connectors 230, 270.

Referring again to FIG. 2, a switch 396 is carried by the mounting plate51. The switch 396 is positioned to be engaged by the base carriage 40when the base carriage 40 has positioned the tower 23 at a centeredposition longitudinally of the table top 21, and to be disengaged by thebase carriage 40 when the base carriage 40 is in an uncentered position.The switch 396 provides a variation in an electrical signal indicativeof when the base carriage 40 is in a centered position.

Referring to FIG. 11, a limit switch 397 is carried atop the Bucky traydrive bar 365. An actuating lever 398 is pivotally mounted by a pin 399and depends through an aperture 366 formed in the bar 365. When the pawl377 is received in the slot 387, the pawl 377 engages the lever 398,pivoting the lever 398 into engagement with the switch 397. When thepawl 377 is removed from the slot 387, the lever 398 pivots under theinfluence of gravity to a position where it disengages the switch 377.The switch 397 is accordingly operative to provide a variation in anelectrical signal indicative of when the Bucky tray drive bar 365 isdrivingly coupled to the upper arm portion 351.

In the preferred practice of the invention, the sensing switches 390,391, 393, 394, 395, 396 and 397 are connected in safety interlockcontrol circuits which will:

(1) When radiographic operation has been selected, retain the carriage24 at a position below that where driving connection is establishedbetween the connectors 230, 270, as sensed by the switch 394, whereby nodriving connection is established between the connectors 230, 270 duringradiography.

(2) Prevent the motor 126 from elevating the carriage 24 to a positionwhere connection is made between the connectors 230, 270 unless:

(a) The tower 23 is centered longitudinally of the table top 21, asindicated by the switch 396;

(b) The tube rotation detent assembly 179 has been unlatched, asindicated by the switch 390;

(c) The extensible arm 25 has been properly retracted for tomographicoperation, as indicated by the switch 391; and,

(d) The arm 25 is properly latched forwardly of the column 23, asindicated by the switch 393.

(3) Prevent the movement of the base carriage 40 from a centeredposition longitudinally of the table top 21 rightwardly to a "tomographready" position as by operation of the motor 55 unless:

(a) The carriage 24 has been elevated to a position where connection hasbeen made between the connectors 230, 270, as indicated by the switch395; and,

(b) The Bucky tray drive bar 365 is drivingly connected to the upper armportion 351, as indicated by the switch 397.

Since circuitry for effecting such safety interconnection of theswitches 390, 391, 393, 394, 395, 396, 397 and the motors 55, 126 isconventional and forms no part of the present invention, it need not bedescribed.

F. Operation of the Tomographic Drive System

In order to facilitate an understanding of the operation of thetomographic drive system, schematic illustrations of certain of thecomponents of the X-ray apparatus 20 are shown in FIGS. 13 and 14. FIG.13 is a side elevational schematic view showing the table top 21, theX-ray source 26 positioned above the table top 21, and the Bucky tray 30positioned beneath the table top 21. FIG. 14 is a top plan schematicview showing the base carriage 40, the track 50 along which the basecarriage 40 moves, the tower 23 supported on the base carriage 40 andthe X-ray source 26. Also shown in FIG. 14 are several of the drivesystem components which interconnect the Bucky tray 30 an the X-raysource 26.

Referring to FIGS. 13 and 14, the numeral 400 designates what will becalled a "center plane." The center plane 400 is a vertical plane whichextends laterally of the table top 21. The axis of the threaded rod 304(FIG. 2) is located within the plane 400.

When a tomograph is to be made, a patient is positioned on the table top21 with the patient's center of interest intersected by the center plane400. The X-ray source 26 and the Bucky tray 30 are then driven back andforth respectively above and below the patient's center of interest toproduce a shadow image of portions of the patient's anatomy which lie inan examination plane extending through the patient's center of interest.One such examination plane is indicated by the numeral 403 in FIG. 13.

Referring to FIG. 13, the path of movement of the X-ray source 26 duringtomography is indicated by the numeral 401. The path of movement of theBucky tray 30 during tomography is indicated in FIG. 13 by the numeral402.

The vertical distance between the paths 401, 402 is the sum of twodistances "A" and "B." The distance "A," as depicted in FIG. 13, is thevertical distance from the path 401 to the examination plane 403. Thedistance "B," as depicted in FIG. 13, is the vertical distance from thepath 402 to the examination plane 403. While the distances "A" and "B"are adjustable to raise or lower the examination plane 403, the sum oftwo distances "A" and "B" is fixed.

The distances "A" and "B" as depicted in FIG. 13 are exactly the samedistances as are indicated by the characters "A" and "B" in FIGS. 2 and14. In FIGS. 2 and 14, the distance "A" is the distance (measuredlaterally of the table top 21) between the axes 284, 327, and thedistance "B" is the distance (measured laterally of the table top 21)between the axes 327, 343.

The distances "A" and "B" can be adjusted by energizing the motor 303 tomove the carriage 320 along the threaded rod 304. As the carriage 320moves along the threaded rod 304, it changes the distance between theaxis 327 and the axes 284, 343. When the carriage 320 positions the axis327 at the location shown in FIG. 2, the central axis of the beam ofX-rays emitted from the source 26 will cross the center plane 400 at apoint 405 (FIG. 13) within the examination plane 403 as the source 26moves back and forth along the path 401.

The position of the examination plane 403 is specified by a distance "C"shown in FIG. 13. The distance "C" is the distance from the table top 21to the examination plane 403. As will be explained, the rotary encoderassembly 336 forms part of a system which provides a digital readout inmillimeters of the position of the examination plane 403. A "zero"reading indicates that the examination plane 403 is coincident with thetable top 21.

The location of a tomographic examination plane 403, i.e., the height ofthe examination plane 403 above the table top 21, is determined by theratio of "A" to "B". If the distance "A" is diminished to a distance"A1," as by operating the drive motor 303 to move the carriage 320rearwardly (rightwardly as viewed in FIG. 2) along the threaded rod 320,the effect will be to cause the arm 282 to pivot through a greater arcabout the axis 284 as the tower 23 moves longitudinally of the table top21 a given distance. The increased arcuate movement of the arm 282 willbe transmitted to the X-ray source 26 through the drive components whichinterconnect the source 26 and the arm 282, causing the source 26 torotate through a greater arc about the axis of the shaft 160 as thetower 23 moves longitudinally of the table top 21 a given distance.Rotation of the source 26 through an increased arc will cause thecentral axis of the beam of X-rays emitted from the source 26 to crossthe center plane 400 at a point 406 above the point 405, therebyestablishing an examination plane above the plane 403.

If the distance "A" is increased to a distance "A2," as by operating thedrive motor 303 to move the carriage 320 forwardly (leftwardly as viewedin FIG. 2) along the threaded rod 320, the effect will be to cause thearm 282 to pivot through a lesser arc about the axis 284 as the tower 23moves longitudinally of the table top 21 a given distance. The decreasedarcuate movement of the arm 282 will be transmitted to the X-ray source26 through the drive components which interconnect the source 26 and thearm 282, causing the source 26 to rotate through a lesser arc about theaxis of the shaft 160 as the tower 23 moves longitudinally of the tabletop 21 a given distance. Rotation of the source 26 through a decreasedarc will cause the central axis of the beam of X-rays emitted from thesource 26 to cross the center plane 400 at a point 407 below the point405, thereby establishing an examination plane below the plane 403.

Regardless of the "A to B" ratio which may be selected, the drivecomponents which interconnect the arm 282 and the Bucky 30 will operateto keep the center of the Bucky tray 30 aligned with the center of theX-ray beam emitted from the source 26. The ratio of the distancesthrough which the source 26 and the Bucky tray 30 move relative to thecenter plane 400 is exactly the ratio "A to B." Hence, if the distance"A" is decreased to raise the examination plane 403, whereby thedistance "B" is correspondingly increased, the travel of the Bucky tray30 along the path 402 will be increased to keep the center of the Buckytray 30 aligned with the center axis of the X-ray beam emitted from thesource 26. Similarly, if the distance "A" is increased to lower theplane of cut 403, whereby the distance "B" is correspondingly decreased,the travel of the Bucky tray 30 along the path 402 will be decreased tokeep the center of the Bucky tray 30 aligned with the center axis of theX-ray beam emitted from the source 26.

Referring to FIG. 2, such an increase or decrease in Bucky tray travelresults because the linear cam 340 constrains the pin 342 to movelongitudinally of the table top 21. The greater the distance "B," thegreater will be the distance traversed by the pin 342 as the tower 23moves longitudinally of the table top 21 a given distance. As has beenexplained, the movement of the pin 342 is transmitted to the Bucky tray30 and in fact represents the exact movement executed by the Bucky tray30 during tomography.

VII. Indication of the Plane of Tomographic Examination by the EncoderAssembly 336

Referring to FIG. 16 the rotary encoder assembly 336 includes agenerally cylindrical housing 451. A pair of end plates 452, 453 closeopposite ends of the housing 451. A pair of bearings 454, 455 arecarried by the end plates 452, 453. A shaft 456 is journaled by thebearings 454, 455. A disc 457 is carried on the shaft 456 at a locationinside the housing 451. A sensor unit 460 is secured to the housing 451.The sensor unit 460 includes a light source 461 and a photocell 462. Thelight source 461 and the photocell 462 are positioned on opposite sidesof the disc 457.

Referring to FIG. 17, three equally spaced slots 463 are formed inperipheral portions of the disc 457. When one of the slots 463 alignswith the light source 461 and the photocell 462, light from the source461 is received by the photocell 462. When none of the slots 463 alignwith the source 461 and the photocell 462, the disc 457 blockstransmission of light from the source 461 to the photocell. By thisarrangement, the photocell 462 provides an intermittent electricalsignal with pulses which indicate the passage of light through one ofthe slots 463. Since the disc 457 carries three of the slots 463, eachrevolution of the disc 457 will provide three pulses in the signal fromthe photocell 462.

The threaded rod 304 has a pitch of three millimeters, which means thateach revolution of the rod 304 is operative to move the carriage 320through a distance of three millimeters. Since the encoder assembly 336provides three signal pulses per revolution, each signal pulse indicatesa one millimeter movement of the carriage 320.

The output signal from the photocell 462 is fed to a digital readoutsystem, indicated generally by the numeral 470 in FIG. 16. The readoutsystem 470 is of conventional construction and includes a digitalreadout scale 471. The scale 471 provides a readout in millimeterswithin the range of 0-250 mm. of the distance "C," i.e., the height of atomographic examination plane above the table top 21. Each pulse fromthe photocell 462 is counted by the system 470 and serves to increase ordecrease the digital reading on the scale 471 by one millimeterdepending on whether the examination plane 403 is being raised orlowered relative to the table top 21. Other circuitry, not shown,connects with system 470 to inform the system about the direction ofrotation of the drive motor 303 so that the system 470 will know whetherthe examination plane 403 is being raised or lowered as the motor 303operates.

VIII. Control of Source Operation During Tomography by the EncoderAssembly 330

The encoder assembly 330 is identical in construction to the encoderassembly 336 except for the arrangement of signaling slots formed in itsshaft-carried disc. Referring to FIG. 18, the disc used in the encoderassembly 330 is indicated generally by the numeral 480. A total of eightslots, 481, 482, 483, 484, 485, 486, 487, 488 are formed in peripheralportions of the disc 480. The slots 481-484 and 485-488 are arrangedsymmetrically about an imaginary line 490 which extends radially of thedisc 480.

The slots 484, 485 are located twelve-and-one-half degrees around thedisc 480 on opposite sides of the line 490, which gives atwenty-five-degree spacing between the slots 484, 485. The slots 483,486 are located twenty-five degrees around the disc 480 on oppositesides of the line 490 which gives a fifty-degree spacing between theslots 483, 486. The slots 482, 487 are located fifty degrees around thedisc 480 on opposite sides of the line 490, which gives aone-hundred-degree spacing between the slots 482, 487. The slots 481,488 are located one-hundred degrees around the disc 480 on oppositesides of the line 490, which gives a two-hundred-degree spacing betweenthe slots 481, 488.

The disc 480 is mounted on the shaft of the rotary encoder assembly 330such that, when the X-ray source 26 and the Bucky tray 30 are located inthe center plane 400, the imaginary line 490 is aligned with the lightsource and the photocell of the encoder assembly 330. Movement of thesource 26 leftwardly or rightwardly of the center plane 400 will causecorresponding counterclockwise or clockwise rotation of the disc 480relative to the source and photocell of the encoder assembly 330.

The ratio of the sizes of the sprockets 328, 329 (FIG. 15) is selectedsuch that the encoder disc 480 rotates through five times the amount ofrotation of the swivel plate 326 relative to the carriage 320. Sincerotation of the swivel plate 326 accurately reflects rotation of thesource 26 about the imaginary pivot axis 405, the encoder disc 480rotates through five times the arc of rotation of the source 26.

If the source 26 pivots back and forth through an arc which extends onlytwo-and-one-half degrees to either side of the center plane 400, theencoder disc will move through a total rotation of twenty-five degreesbetween positions where the slots 484, 485 are selectively aligned withthe source and photocell of the encoder assembly 300. The signalsprovided by the photocell of the encoder assembly 330 when the slots484, 485 transmit light to the encoder photocell can be used to startand stop the source 26 so that the source is active through only afive-degree range of movement. A tomography procedure of this type iscalled "zonography" and is used where a thick examination plane of cutis desired and where only peripheral details are desirably blurred inthe resulting image.

Signals provided by the photocell of the encoder assembly 330 whenothers of the slots 481-488 transmit light to the encoder photocell canbe used to start and stop the source 26 so that the source is activethrough such ranges of movement as ten degrees, twenty degrees and fortydegrees. The larger is the range of active source movement, the thinneris the resulting examination plane of cut. A forty-degree range ofactive source movement will, for example, leave a clear image ofanatomical portions which lie within about a one-millimeter thickexamination plane of cut.

Suitable electronic circuitry of conventional design connects with theencoder assembly 330 and with the source 26 such that:

(1) If a five-degree exposure angle is desired, as for zonography, thesource 26 is energized between the fourth and fifth pulses of theencoder 330 which result from an alignment of the disc slots 484, 485with the encoder light source and photocell;

(2) If a ten-degree exposure angle is desired, the source 26 isenergized between the third and sixth encoder pulses, which correspondto the disc slots 483, 486;

(3) If a twenty-degree exposure angle is desired, the source 26 isenergized between the second and seventh encoder pulses, whichcorrespond to the disc slots 482, 487; and,

(4) If a forty-degree exposure angle is desired, the source 26 isenergized between the first and eighth encoder pulses, which correspondto the disc slots 481, 488.

IX. Operation of the Apparatus 20 During Radiography

The apparatus 20 is easily converted from tomographic to radiographicoperation simply by:

(1) Lowering the carriage 24 to disconnect the connectors 230, 270; and,

(2) Energizing the solenoid 371 (FIG. 1) to disconnect the Bucky traydrive bar 365 from the upper arm portion 351.

Once these simple steps are complete, the source 26 and the Bucky tray30 may be moved independently relative to each other and relative to thetable top 21 for the taking of conventional radiographs.

Converting the apparatus 20 from radiographic operation to tomographicoperation is accomplished by:

(1) De-energizing the solenoid 371 and moving the Bucky tray 30 to acentered position along the table top 21 where the pawl 377 pivots intothe slot 387 to lock the Bucky drive bar 365 to the upper arm portion351;

(2) Raising the carriage 24 to connect the connectors 230, 270; and,

(3) Moving the tower 23 rightwardly to a position of readiness forinitiating the production of a tomograph.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:
 1. In a tomographic X-ray table including a base, anx-ray source and an imaging assembly the improved tomographic drivesystem comprising:(a) a movably supported carriage positioned within thebase; (b) an extensible proportioning arm movably connected to saidcarriage for rotation about an axis within the base; (c) the arm havingopposite end regions adapted to be connected to a tower structure andanother structure for driving the structures through coordinatedmovements to produce a tomograph, the structures being constrained formovement along parallel paths; (d) said carriage being movablesubstantially rectilinearly within the base to control the location ofthe axis; and, (e) sliding guide means interposed between the arm andthe carriage to permit relative carriage and arm movement longitudinallyof the arm as the arm rotates about said axis.
 2. An X-ray apparatuscomprising:(a) an upstanding base structure; (b) a patient supportcarried by the base structure and defining an elongated, substantiallyhorizontal patient support surface; (c) a base carriage movablysupported on the base structure for movement longitudinally of the basestructure; (d) an upstanding tower carried on the base carriage formovement longitudinally of the patient support surface as the basecarriage moves longitudinally of the base structure; (e) a towercarriage movably supported on the tower at a position above the supportsurface for movement toward and away from the support surface; (f) anextensible arm carried on the tower carriage and extending over thesupport surface, the arm being rotatable relative to the carriage aroundthe tower, and being extensible in directions toward and away from thetower; (g) an X-ray source carried on the extensible arm at a positionoverlying the support surface, the source being movable toward and awayfrom the tower as the arm extends and retracts, and being rotatablerelative to the arm about an axis extending substantially parallel tothe plane of the support surface; (h) first rotatable drive meansextending through the arm, such first drive means having one end regionconnected to the source and being rotatable with the source as thesource rotates about said axis, and having an opposite end regionpositioned near the tower; (i) second rotatable drive means extendingthrough the tower and having one end region positioned to be engaged bysaid first drive means only when the carriage is at a predeterminedposition along the tower, and having an opposite end region positionednear the lower end of the tower; p1 (j) proportioning arm means havingone end region connected to said other end region of said second drivemeans and extending from the lower end region of the tower into the basestructure; (k) an X-ray imaging device carried within the base structureand being movable longitudinally of the base structure; (l) releasableconnection means releasably connecting an opposite end region of theproportioning arm means to the imaging device; (m) said first and seconddrive means, said proportioning arm means, and said connection meansbeing operative when interconnecting the source and the device tocoordinate the movement of the source and the device such that an X-raybeam emanating from the source through a patient positioned on thesupport surface and received by the device will produce a tomographrepresentative of a plane of cut through such patient.
 3. The apparatusof claim 2 additionally including means carried within the basestructure for adjusting the proportioning arm means to control thelocation of such plane of cut.
 4. In a tomographic table having a baseand tower and film supporting structures respectively mounted formovement longitudinally of the table, a drive control assemblycomprising:(a) a carriage movably mounted in the base and beneath apatient-supporting surface of the table, the carriage being movable in aplane; (b) a first arm means pivotally connected to the carriage in thebase and to the tower structure; (c) a second arm means in the base andpivotally connected to the carriage and the film supporting structure;(d) drive means connected to at least a selected one of the structuresand arm means for causing opposed structure movement at least partiallycontrolled by the arm means; and, (e) adjustment means connected to thecarriage to move the carriage and adjust the location of one of thepivotal connections so as to adjust the amount of relative arm movementand the extent of the opposed structure movement.
 5. The table of claim4 wherein the spacing between the pivotal connections of at least one ofsaid arm means changes as the structures are driven in their opposedmovement and wherein the assembly includes elements for achievingextension and contraction of the effective length of said one arm meansto maintain its pivotal connections as the pivotal spacing changes. 6.An X-ray tomography apparatus, comprising:(a) a base; (b) a patientsupport carried by the base and defining a patient support surface; (c)a pair of X-ray devices, one of said devices being an X-ray source, andthe other of said devices being an X-ray imaging assembly; (d) a firststructure movably carried by the base for supporting one of the deviceson one side of said surface; (e) a second structure movably carried bythe base for supporting the other of the devices on the opposite side ofsuch surface; (f) drive means interconnecting said structures to movesaid devices through coordinated movements with the source beingangulated to keep an X-ray beam emanating therefrom aligned with theimaging assembly for production of a tomographic image; (g) said drivemeans including:(i) carriage means movably supported within and by saidbase; (ii) an extensible proportioning arm movably connected to saidcarriage means; (iii) opposite end regions of said arm being connectedto separate ones of said structures; (iv) adjustable linkage meanshoused within the base substantially entirely beneath said surface foreffecting movement of said carriage means along a path such thatmovement of the carriage means controls the location of an axis aboutwhich said arm pivots relative to said carriage means and selects thelocation of the tomographic examination plane of a tomograph producedduring coordinated movement of the devices; and, (v) opposite endregions of said arm being movable in opposite directions as said armpivots about said axis so that said arm effects movement of saidstructures in opposite directions.
 7. The apparatus of claim 6 whereinsaid drive means additionally includes means constraining the oppositeend regions of said arm to translate along parallel paths as said armpivots about said axis.
 8. The apparatus of claim 7 wherein:(a) saidcarriage means includes a swivel structure movably supported to pivotabout said axis; (b) said arm includes a pair of arm members slidablycoupled to said swivel structure for extension and retraction in a planewhich includes said axis; and, (c) said swivel structure is movablesubstantially orthogonally between said paths to position said axis toobtain a desired ratio of movement of said structures as said arm pivotsabout said axis.
 9. An X-ray apparatus comprising:(a) a base structure;(b) a patient support carried by the base structure and defining ahorizontal patient support surface; (c) a tower carried by the base formovement longitudinally of the patient support surface; (d) a towercarriage movably supported on the tower at a position above the supportsurface for movement toward and away from the support surface; (e) anarm carried by the tower carriage and extending over the supportsurface; (f) an X-ray source carried by the arm at a position overlyingthe support surface, the source mounted for rotation relative to thetower about an axis extending substantially parallel to the supportsurface; (g) first rotatable drive means extending through the arm, suchfirst drive means having one end region connected to the source andbeing rotatable with the source as the source rotates about said axis,and having an opposite end region positioned near the tower; (h) secondrotatable drive means extending through the tower and having one endregion positioned to be engaged by said first drive means only when thetower carriage is at a predetermined position along the tower, andhaving an opposite end region positioned near the lower end of thetower; (i) proportioning arm means having one end region connected tosaid second drive means and extending from the lower end region of thetower into the base structure; (j) an X-ray imaging device carriedwithin the base structure and being movable longitudinally of the basestructure; (k) releasable connection means releasably connecting anopposite end region of the proportioning arm means to the imagingdevice; and, (l) said first and second drive means, said proportioningarm means, and said connection means being operative wheninterconnecting the source and the device to coordinate the movement ofthe source and the device such that an X-ray beam emanating from thesource through a patient positioned on the support surface and receivedby the device will produce a tomograph representative of the planethrough such patient.
 10. The apparatus of claim 9 additionallyincluding means carried within the base structure for adjusting theproportioning arm means to control the location of such plane.
 11. AnX-ray apparatus comprising:(a) a base structure including a patientsupport surface; (b) a tower mounted for movement longitudinally of thepatient support surface; (c) a tower carriage movably supported on thetower at a position above the support surface for movement toward andaway from the support surface; (d) an arm carried by the tower carriageand extending over the support surface; (e) an X-ray source devicecarried on the arm at a position overlying the support surface, thesource being rotatable relative to the tower about an axis extendingsubstantially parallel to the support surface; (f) first drive meansextending through the arm; (g) second drive means extending through thetower and having one end region positioned near said first drive meansand having an opposite end region positioned near the lower end of thetower; (h) proportioning arm means substantially within the base andhaving one end region near said second drive means; (i) an X-ray imagingdevice carried within the base structure and being movablelongitudinally of the base structure; (j) connection means forconnecting an opposite end region of the proportioning arm means to theimaging device; (k) certain of said means including structure forselectively establishing a driving interconnection through said meansbetween said devices under a selected and predetermined operatingcondition; and, (1) said first and second drive means, saidproportioning arm means, and said connection means being operative wheninterconnecting the devices to coordinate the movement of the devicessuch that an X-ray beam emanating from the source through a patientpositioned on the support surface and received by the device willproduce an image of a tomograph plane.
 12. The apparatus of claim 11additionally including means carried within the base structure foradjusting the proportioning arm means to control the location of suchplane.
 13. An X-ray tomography apparatus, comprising:(a) a base; (b) apatient support carried by the base and defining a patient supportsurface; (c) a pair of X-ray devices, one of said devices being an X-raysource, and the other of said devices being an X-ray imaging assembly;(d) a first structure movably carried by the base for supporting one ofthe devices on one side of such surface; (e) a second structure movablycarried by the base for supporting the other of the devices on theopposite side of such surface; (f) drive means interconnecting saidstructures to move said devices through coordinated movements with thesource being angulated to keep an X-ray beam emanating therefrom alignedwith the imaging assembly for production of a tomographic image; and,(g) said drive means including adjustable linkage means, housed withinthe base and beneath the patient support surface, for selecting thelocation of the tomographic examination plane of a tomograph producedduring coordinated movement of the devices.
 14. The apparatus of claim13 additionally including sensor means for providing a signal indicativeof the location of the tomographic examination plane.
 15. The apparatusof claim 14 wherein said sensor means includes a member rotatablyconnected to said linkage means and having at least one formed signalproducing portion, said member being operable to rotate said portionaround a substantially circular path in response to repositioning ofsaid tomographic examination plane, and signalling means positionedalong said path and being operable in response to movement of saidportion to provide an output signal.
 16. The apparatus of claim 13including a sensor means having a member connected to said drive meansand having at least one formed portion, said member being operable tomove said portion along a path in response to movement of said onedevice, and signalling means positioned along said path and beingoperable in response to movement of said portion to provide an outputsignal.
 17. The apparatus of claim 13 additionally including sensormeans for providing a pulsed electrical output signal indicative of theposition of at least one of said devices.
 18. The apparatus of claim 13wherein(a) said first structure includes a tower extending orthoganallyof the patient support; and, (b) said drive means includes componentswhich extend through the tower associated with said source and connectwith said source to effect such source angulation.
 19. The apparatus ofclaim 13 additionally including sensor and readout means for producingan indication of the location of said tomographic examination plane. 20.The apparatus of claim 13 wherein said source is movable along saidassociated structure and certain of said components are connectable in adriving relationship only when said source is positioned in apredetermined location along said associated structure and aredisconnected when said source is positioned out of said predeterminedlocation.
 21. The apparatus of claim 13 wherein said drive meansincludes:(a) carriage means movably supported by said base; (b) anextensible proportioning arm movably connected to said carriage means;(c) opposite end regions of said arm being connected to separate ones ofsaid structures; and, (d) said carriage means being movable within saidbase to control the location of an axis about which said arm pivotsrelative to said carriage means.
 22. The apparatus of claim 21 whereinsaid drive means additionally includes means constraining opposite endregions of said arm to translate along parallel paths as said arm pivotsabout said axis.
 23. The apparatus of claim 22 wherein:(a) said carriagemeans includes a swivel structure movably supported to pivot about saidaxis; (b) said arm includes a pair of arm members slidably coupled tosaid swivel structure for extension and retraction in a plane whichincludes said axis; and, (c) said swivel structure is movablesubstantially orthogonally between said paths to position said axis toobtain a desired ratio of movement of said structures as said arm pivotsabout said axis.
 24. An X-ray apparatus operable for tomography,comprising:(a) a base structure; (b) an elongated patient supportcarried by the base structure and defining a substantially horizontallyextending patient positioning surface; (c) an upstanding tower structurecarried by the base structure for movement longitudinally of the patientsupport; (d) an X-ray source supported on the tower structure at aposition overlying the positioning surface; (e) an X-ray imaging devicecarried within the base structure beneath the positioning surface andmovable longitudinally beneath such surface; (f) a powered driveinterconnecting the source and the device to move the source and thedevice through coordinated movements with the source being angulated tokeep an X-ray beam emanating therefrom aligned with the device forproduction of a tomograph; and, (g) said drive including an adjustablelinkage means disposed within the base structure and beneath thepositioning surface for selecting the location of the plane of atomograph produced during coordinated movement of the source and thedevice.
 25. The apparatus of claim 24 wherein said drive includescomponents which extend through said tower structure and connect withsaid source to effect such source angulation.
 26. The apparatus of claim24 wherein said tower includes an upstanding column and an arm whichextends from said column over said surface to support the source, andsaid drive includes components extending through said column and throughsaid arm.
 27. The apparatus of claim 26 wherein said arm is movablealong said column toward and away from said surface, and wherein certainof the components carried in said arm and other of the components arecarried in said column, and wherein a connection can be formed betweensaid certain and other components only when said arm is at apredetermined position.
 28. The apparatus of claim 24 wherein an armcarries the source and the arm is rotatable around an upstanding columnof said tower, and disconnect means are provided to permit rotation ofsaid arm around said column.
 29. The apparatus of claim 28 wherein:(a) alatch structure is provided to normally prevent rotation of said armaround said column; and, (b) control means is provided to operate saiddisconnect means and to unlatch said latch structure to permit rotationof said arm.
 30. The apparatus of claim 24 wherein said driveincludes:(a) carriage means movably supported within said base; (b) anextensible proportioning arm movably connected to said carriage means;(c) opposite end regions of said arm being connected to said towerstructure and said device; (d) said carriage means being movable tocontrol the location of an axis about which said arm pivots; (e) wherebythe position of said carriage means determines the ratio of relativemovements longitudinally of said patient support executed by said towerstructure and said device.
 31. The apparatus of claim 30 wherein:(a)said carriage means includes a swivel structure movably supported topivot about said axis; (b) said arm includes a pair of arm membersslidably coupled to said swivel structure for extension and retractionin a common plane which includes said axis; and, (c) said swivelstructure is movable substantially orthogonally of the path of saidimaging device to position said axis.
 32. The apparatus of claim 30wherein:(a) said drive includes rotatable components which extendthrough said tower structure and connect with said source to effectangulation of said source; and, (b) said proportioning arm is drivinglyconnected to such components to rotate such components and therebyangulate said source in response to pivotal movement of said arm aboutsaid axis.
 33. An X-ray apparatus including a base and a patientsupport, the improvement comprising an X-ray source, an X-ray imagingdevice, a framework including a pair of legs and a connecting stem whichinterconnect and position the source and the device on opposite sides ofa patient support, and drive means housed within and shielded frompatient contact by said framework and the base for moving the source andthe device through coordinated movements in opposite directions in orderto produce a tomograph, one of said legs being disposed within the base,said drive means including a proportioning arm housed within said baseand coactable with said one leg for effecting proportional movements inopposite directions of the source and the device.
 34. The apparatus ofclaim 33 wherein said drive means additionally includes driveinterconnected components carried in the other of said legs and in saidstem, said components interconnecting said proportioning arm and saidsource to angulate said source as said source and said device move inopposite directions to keep an X-ray beam emanating from said sourcedirected toward said device.
 35. The apparatus of claim 33 additionallyincluding means movably supported within said base to selectivelyposition an axis about which said proportioning arm pivots, and tocontrol the position of a tomographic imaging plane.
 36. The apparatusof claim 33 additionally including latch means interposed between theother of said legs and said source to selectively lock said source andthereby prevent its rotation relative to said other leg.
 37. Theapparatus of claim 33 wherein said other leg is movable along said stem,and certain drive means components are connectable only when said arm isin a predetermined position along said stem.
 38. The apparatus of claim37 wherein a power means is provided within said framework to effectmovement of said other leg along said stem.
 39. The apparatus of claim33 wherein the other of said legs is extensible to position said sourcerelatively toward and away from said stem.
 40. The apparatus of claim 39wherein a power means is provided within said framework to extend andretract said other leg.